MongoDB query convert in to PHP? - php

Question

I am having trouble converting it to PHP. My query is working in mongodb and get output well. But same query i tried to convert into php shown error
Array
(
[ok] => 0
[errmsg] => A pipeline stage specification object must contain exactly one field.
[code] => 16435
)
My collection sample as follows
{
"_id" : ObjectId("5790f9407ffbe031fa2049e3"),
"EventTS" : ISODate("2016-07-01T04:30:00.000+0530"),
"KeyValues" : [
{
"InputVolt" : null
},
{
"InputVolt" : 250
},
{
"InputVolt" : 230
},
{
"InputVolt" : 230
},
{
"InputVolt" : 240
}
]
},
{
"_id" : ObjectId("5790f9407ffbe031fa2049e4"),
"EventTS" : ISODate("2016-07-01T04:35:00.000+0530"),
"KeyValues" : [
{
"InputVolt" : null
},
{
"InputVolt" : 260
},
{
"InputVolt" : null
},
{
"InputVolt" : null
},
{
"InputVolt" : null
}
]
}
My mongodb query is
db.sample_coll.aggregate(
{
$unwind: {
path:"$KeyValues",
includeArrayIndex:"arrayIndex",
preserveNullAndEmptyArrays:true
}
},
{
$project: {
timestamp:{
"$add":["$EventTS",{"$multiply":[60000,"$arrayIndex"]}]
} ,
"InputVolt":"$KeyValues.InputVolt",
arrayIndex:1
}
},
{
$match: {
$and: [
{InputVolt: {$ne: null}}
]
}
}
);
My mongo query convert into php as follows
$pipeline = array(
array('$unwind' =>
array( 'path' => '$KeyValues'),
array( 'includeArrayIndex' => 'arrayIndex' ),
array( 'preserveNullAndEmptyArrays' => 'true' )
),
array(
'$project' => array(
'timestamp' => array(
'$add' => array(
'$EventTS',
array('$multiply' => array( 60000, '$arrayIndex' ))
)
),
array( 'InputVolt' => array( '$KeyValues', 'InputVolt' ) ) ,
array('arrayIndex' => 1)
)
),
array(
'$match' => array(
'$and' => array(
array('InputVolt' => array('$ne' => null )),
)
)
)
);
$result = $collection->aggregate($pipeline);
I don't know what happen. Please suggest me.